/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Pattern;
import javax.annotation.CheckForNull;

/**
 * Extracts non-overlapping substrings from an input string, typically by recognizing appearances of
 * a <i>separator</i> sequence. This separator can be specified as a single {@linkplain #on(char)
 * character}, fixed {@linkplain #on(String) string}, {@linkplain #onPattern regular expression} or
 * {@link #on(CharMatcher) CharMatcher} instance. Or, instead of using a separator at all, a
 * splitter can extract adjacent substrings of a given {@linkplain #fixedLength fixed length}.
 *
 * <p>For example, this expression:
 *
 * <pre>{@code
 * Splitter.on(',').split("foo,bar,qux")
 * }</pre>
 * <p>
 * ... produces an {@code Iterable} containing {@code "foo"}, {@code "bar"} and {@code "qux"}, in
 * that order.
 *
 * <p>By default, {@code Splitter}'s behavior is simplistic and unassuming. The following
 * expression:
 *
 * <pre>{@code
 * Splitter.on(',').split(" foo,,,  bar ,")
 * }</pre>
 * <p>
 * ... yields the substrings {@code [" foo", "", "", " bar ", ""]}. If this is not the desired
 * behavior, use configuration methods to obtain a <i>new</i> splitter instance with modified
 * behavior:
 *
 * <pre>{@code
 * private static final Splitter MY_SPLITTER = Splitter.on(',')
 *     .trimResults()
 *     .omitEmptyStrings();
 * }</pre>
 *
 * <p>Now {@code MY_SPLITTER.split("foo,,, bar ,")} returns just {@code ["foo", "bar"]}. Note that
 * the order in which these configuration methods are called is never significant.
 *
 * <p><b>Warning:</b> Splitter instances are immutable. Invoking a configuration method has no
 * effect on the receiving instance; you must store and use the new splitter instance it returns
 * instead.
 *
 * <pre>{@code
 * // Do NOT do this
 * Splitter splitter = Splitter.on('/');
 * splitter.trimResults(); // does nothing!
 * return splitter.split("wrong / wrong / wrong");
 * }</pre>
 *
 * <p>For separator-based splitters that do not use {@code omitEmptyStrings}, an input string
 * containing {@code n} occurrences of the separator naturally yields an iterable of size {@code n +
 * 1}. So if the separator does not occur anywhere in the input, a single substring is returned
 * containing the entire input. Consequently, all splitters split the empty string to {@code [""]}
 * (note: even fixed-length splitters).
 *
 * <p>Splitter instances are thread-safe immutable, and are therefore safe to store as {@code static
 * final} constants.
 *
 * <p>The {@link Joiner} class provides the inverse operation to splitting, but note that a
 * round-trip between the two should be assumed to be lossy.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/StringsExplained#splitter">{@code Splitter}</a>.
 *
 * @author Julien Silland
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 1.0
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public final class Splitter
{
    private final CharMatcher trimmer;
    private final boolean omitEmptyStrings;
    private final Strategy strategy;
    private final int limit;

    private Splitter(Strategy strategy)
    {
        this(strategy, false, CharMatcher.none(), Integer.MAX_VALUE);
    }

    private Splitter(Strategy strategy, boolean omitEmptyStrings, CharMatcher trimmer, int limit)
    {
        this.strategy = strategy;
        this.omitEmptyStrings = omitEmptyStrings;
        this.trimmer = trimmer;
        this.limit = limit;
    }

    /**
     * Returns a splitter that uses the given single-character separator. For example, {@code
     * Splitter.on(',').split("foo,,bar")} returns an iterable containing {@code ["foo", "", "bar"]}.
     *
     * @param separator the character to recognize as a separator
     * @return a splitter, with default settings, that recognizes that separator
     */
    public static Splitter on(char separator)
    {
        return on(CharMatcher.is(separator));
    }

    /**
     * Returns a splitter that considers any single character matched by the given {@code CharMatcher}
     * to be a separator. For example, {@code
     * Splitter.on(CharMatcher.anyOf(";,")).split("foo,;bar,quux")} returns an iterable containing
     * {@code ["foo", "", "bar", "quux"]}.
     *
     * @param separatorMatcher a {@link CharMatcher} that determines whether a character is a
     *                         separator
     * @return a splitter, with default settings, that uses this matcher
     */
    public static Splitter on(final CharMatcher separatorMatcher)
    {
        checkNotNull(separatorMatcher);

        return new Splitter(
                new Strategy()
                {
                    @Override
                    public SplittingIterator iterator(Splitter splitter, final CharSequence toSplit)
                    {
                        return new SplittingIterator(splitter, toSplit)
                        {
                            @Override
                            int separatorStart(int start)
                            {
                                return separatorMatcher.indexIn(toSplit, start);
                            }

                            @Override
                            int separatorEnd(int separatorPosition)
                            {
                                return separatorPosition + 1;
                            }
                        };
                    }
                });
    }

    /**
     * Returns a splitter that uses the given fixed string as a separator. For example, {@code
     * Splitter.on(", ").split("foo, bar,baz")} returns an iterable containing {@code ["foo",
     * "bar,baz"]}.
     *
     * @param separator the literal, nonempty string to recognize as a separator
     * @return a splitter, with default settings, that recognizes that separator
     */
    public static Splitter on(final String separator)
    {
        checkArgument(separator.length() != 0, "The separator may not be the empty string.");
        if (separator.length() == 1)
        {
            return Splitter.on(separator.charAt(0));
        }
        return new Splitter(
                new Strategy()
                {
                    @Override
                    public SplittingIterator iterator(Splitter splitter, CharSequence toSplit)
                    {
                        return new SplittingIterator(splitter, toSplit)
                        {
                            @Override
                            public int separatorStart(int start)
                            {
                                int separatorLength = separator.length();

                                positions:
                                for (int p = start, last = toSplit.length() - separatorLength; p <= last; p++)
                                {
                                    for (int i = 0; i < separatorLength; i++)
                                    {
                                        if (toSplit.charAt(i + p) != separator.charAt(i))
                                        {
                                            continue positions;
                                        }
                                    }
                                    return p;
                                }
                                return -1;
                            }

                            @Override
                            public int separatorEnd(int separatorPosition)
                            {
                                return separatorPosition + separator.length();
                            }
                        };
                    }
                });
    }

    /**
     * Returns a splitter that considers any subsequence matching {@code pattern} to be a separator.
     * For example, {@code Splitter.on(Pattern.compile("\r?\n")).split(entireFile)} splits a string
     * into lines whether it uses DOS-style or UNIX-style line terminators.
     *
     * @param separatorPattern the pattern that determines whether a subsequence is a separator. This
     *                         pattern may not match the empty string.
     * @return a splitter, with default settings, that uses this pattern
     * @throws IllegalArgumentException if {@code separatorPattern} matches the empty string
     */
    @GwtIncompatible // java.util.regex
    public static Splitter on(Pattern separatorPattern)
    {
        return on(new JdkPattern(separatorPattern));
    }

    private static Splitter on(final CommonPattern separatorPattern)
    {
        checkArgument(
                !separatorPattern.matcher("").matches(),
                "The pattern may not match the empty string: %s",
                separatorPattern);

        return new Splitter(
                new Strategy()
                {
                    @Override
                    public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit)
                    {
                        final CommonMatcher matcher = separatorPattern.matcher(toSplit);
                        return new SplittingIterator(splitter, toSplit)
                        {
                            @Override
                            public int separatorStart(int start)
                            {
                                return matcher.find(start) ? matcher.start() : -1;
                            }

                            @Override
                            public int separatorEnd(int separatorPosition)
                            {
                                return matcher.end();
                            }
                        };
                    }
                });
    }

    /**
     * Returns a splitter that considers any subsequence matching a given pattern (regular expression)
     * to be a separator. For example, {@code Splitter.onPattern("\r?\n").split(entireFile)} splits a
     * string into lines whether it uses DOS-style or UNIX-style line terminators. This is equivalent
     * to {@code Splitter.on(Pattern.compile(pattern))}.
     *
     * @param separatorPattern the pattern that determines whether a subsequence is a separator. This
     *                         pattern may not match the empty string.
     * @return a splitter, with default settings, that uses this pattern
     * @throws IllegalArgumentException if {@code separatorPattern} matches the empty string or is a
     *                                  malformed expression
     */
    @GwtIncompatible // java.util.regex
    public static Splitter onPattern(String separatorPattern)
    {
        return on(Platform.compilePattern(separatorPattern));
    }

    /**
     * Returns a splitter that divides strings into pieces of the given length. For example, {@code
     * Splitter.fixedLength(2).split("abcde")} returns an iterable containing {@code ["ab", "cd",
     * "e"]}. The last piece can be smaller than {@code length} but will never be empty.
     *
     * <p><b>Note:</b> if {@link #fixedLength} is used in conjunction with {@link #limit}, the final
     * split piece <i>may be longer than the specified fixed length</i>. This is because the splitter
     * will <i>stop splitting when the limit is reached</i>, and just return the final piece as-is.
     *
     * <p><b>Exception:</b> for consistency with separator-based splitters, {@code split("")} does not
     * yield an empty iterable, but an iterable containing {@code ""}. This is the only case in which
     * {@code Iterables.size(split(input))} does not equal {@code IntMath.divide(input.length(),
     * length, CEILING)}. To avoid this behavior, use {@code omitEmptyStrings}.
     *
     * @param length the desired length of pieces after splitting, a positive integer
     * @return a splitter, with default settings, that can split into fixed sized pieces
     * @throws IllegalArgumentException if {@code length} is zero or negative
     */
    public static Splitter fixedLength(final int length)
    {
        checkArgument(length > 0, "The length may not be less than 1");

        return new Splitter(
                new Strategy()
                {
                    @Override
                    public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit)
                    {
                        return new SplittingIterator(splitter, toSplit)
                        {
                            @Override
                            public int separatorStart(int start)
                            {
                                int nextChunkStart = start + length;
                                return (nextChunkStart < toSplit.length() ? nextChunkStart : -1);
                            }

                            @Override
                            public int separatorEnd(int separatorPosition)
                            {
                                return separatorPosition;
                            }
                        };
                    }
                });
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter, but automatically omits
     * empty strings from the results. For example, {@code
     * Splitter.on(',').omitEmptyStrings().split(",a,,,b,c,,")} returns an iterable containing only
     * {@code ["a", "b", "c"]}.
     *
     * <p>If either {@code trimResults} option is also specified when creating a splitter, that
     * splitter always trims results first before checking for emptiness. So, for example, {@code
     * Splitter.on(':').omitEmptyStrings().trimResults().split(": : : ")} returns an empty iterable.
     *
     * <p>Note that it is ordinarily not possible for {@link #split(CharSequence)} to return an empty
     * iterable, but when using this option, it can (if the input sequence consists of nothing but
     * separators).
     *
     * @return a splitter with the desired configuration
     */
    public Splitter omitEmptyStrings()
    {
        return new Splitter(strategy, true, trimmer, limit);
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter but stops splitting after
     * it reaches the limit. The limit defines the maximum number of items returned by the iterator,
     * or the maximum size of the list returned by {@link #splitToList}.
     *
     * <p>For example, {@code Splitter.on(',').limit(3).split("a,b,c,d")} returns an iterable
     * containing {@code ["a", "b", "c,d"]}. When omitting empty strings, the omitted strings do not
     * count. Hence, {@code Splitter.on(',').limit(3).omitEmptyStrings().split("a,,,b,,,c,d")} returns
     * an iterable containing {@code ["a", "b", "c,d"}. When trim is requested, all entries are
     * trimmed, including the last. Hence {@code Splitter.on(',').limit(3).trimResults().split(" a , b
     * , c , d ")} results in {@code ["a", "b", "c , d"]}.
     *
     * @param maxItems the maximum number of items returned
     * @return a splitter with the desired configuration
     * @since 9.0
     */
    public Splitter limit(int maxItems)
    {
        checkArgument(maxItems > 0, "must be greater than zero: %s", maxItems);
        return new Splitter(strategy, omitEmptyStrings, trimmer, maxItems);
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter, but automatically
     * removes leading and trailing {@linkplain CharMatcher#whitespace whitespace} from each returned
     * substring; equivalent to {@code trimResults(CharMatcher.whitespace())}. For example, {@code
     * Splitter.on(',').trimResults().split(" a, b ,c ")} returns an iterable containing {@code ["a",
     * "b", "c"]}.
     *
     * @return a splitter with the desired configuration
     */
    public Splitter trimResults()
    {
        return trimResults(CharMatcher.whitespace());
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter, but removes all leading
     * or trailing characters matching the given {@code CharMatcher} from each returned substring. For
     * example, {@code Splitter.on(',').trimResults(CharMatcher.is('_')).split("_a ,_b_ ,c__")}
     * returns an iterable containing {@code ["a ", "b_ ", "c"]}.
     *
     * @param trimmer a {@link CharMatcher} that determines whether a character should be removed from
     *                the beginning/end of a subsequence
     * @return a splitter with the desired configuration
     */
    // TODO(kevinb): throw if a trimmer was already specified!
    public Splitter trimResults(CharMatcher trimmer)
    {
        checkNotNull(trimmer);
        return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
    }

    /**
     * Splits {@code sequence} into string components and makes them available through an {@link
     * Iterator}, which may be lazily evaluated. If you want an eagerly computed {@link List}, use
     * {@link #splitToList(CharSequence)}.
     *
     * @param sequence the sequence of characters to split
     * @return an iteration over the segments split from the parameter
     */
    public Iterable<String> split(final CharSequence sequence)
    {
        checkNotNull(sequence);

        return new Iterable<String>()
        {
            @Override
            public Iterator<String> iterator()
            {
                return splittingIterator(sequence);
            }

            @Override
            public String toString()
            {
                return Joiner.on(", ")
                        .appendTo(new StringBuilder().append('['), this)
                        .append(']')
                        .toString();
            }
        };
    }

    private Iterator<String> splittingIterator(CharSequence sequence)
    {
        return strategy.iterator(this, sequence);
    }

    /**
     * Splits {@code sequence} into string components and returns them as an immutable list. If you
     * want an {@link Iterable} which may be lazily evaluated, use {@link #split(CharSequence)}.
     *
     * @param sequence the sequence of characters to split
     * @return an immutable list of the segments split from the parameter
     * @since 15.0
     */
    public List<String> splitToList(CharSequence sequence)
    {
        checkNotNull(sequence);

        Iterator<String> iterator = splittingIterator(sequence);
        List<String> result = new ArrayList<>();

        while (iterator.hasNext())
        {
            result.add(iterator.next());
        }

        return Collections.unmodifiableList(result);
    }

    /**
     * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
     * into keys and values using the specified separator.
     *
     * @since 10.0
     */
    @Beta
    public MapSplitter withKeyValueSeparator(String separator)
    {
        return withKeyValueSeparator(on(separator));
    }

    /**
     * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
     * into keys and values using the specified separator.
     *
     * @since 14.0
     */
    @Beta
    public MapSplitter withKeyValueSeparator(char separator)
    {
        return withKeyValueSeparator(on(separator));
    }

    /**
     * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
     * into keys and values using the specified key-value splitter.
     *
     * <p>Note: Any configuration option configured on this splitter, such as {@link #trimResults},
     * does not change the behavior of the {@code keyValueSplitter}.
     *
     * <p>Example:
     *
     * <pre>{@code
     * String toSplit = " x -> y, z-> a ";
     * Splitter outerSplitter = Splitter.on(',').trimResults();
     * MapSplitter mapSplitter = outerSplitter.withKeyValueSeparator(Splitter.on("->"));
     * Map<String, String> result = mapSplitter.split(toSplit);
     * assertThat(result).isEqualTo(ImmutableMap.of("x ", " y", "z", " a"));
     * }</pre>
     *
     * @since 10.0
     */
    @Beta
    public MapSplitter withKeyValueSeparator(Splitter keyValueSplitter)
    {
        return new MapSplitter(this, keyValueSplitter);
    }

    /**
     * An object that splits strings into maps as {@code Splitter} splits iterables and lists. Like
     * {@code Splitter}, it is thread-safe and immutable. The common way to build instances is by
     * providing an additional {@linkplain Splitter#withKeyValueSeparator key-value separator} to
     * {@link Splitter}.
     *
     * @since 10.0
     */
    @Beta
    public static final class MapSplitter
    {
        private static final String INVALID_ENTRY_MESSAGE = "Chunk [%s] is not a valid entry";
        private final Splitter outerSplitter;
        private final Splitter entrySplitter;

        private MapSplitter(Splitter outerSplitter, Splitter entrySplitter)
        {
            this.outerSplitter = outerSplitter; // only "this" is passed
            this.entrySplitter = checkNotNull(entrySplitter);
        }

        /**
         * Splits {@code sequence} into substrings, splits each substring into an entry, and returns an
         * unmodifiable map with each of the entries. For example, {@code
         * Splitter.on(';').trimResults().withKeyValueSeparator("=>").split("a=>b ; c=>b")} will return
         * a mapping from {@code "a"} to {@code "b"} and {@code "c"} to {@code "b"}.
         *
         * <p>The returned map preserves the order of the entries from {@code sequence}.
         *
         * @throws IllegalArgumentException if the specified sequence does not split into valid map
         *                                  entries, or if there are duplicate keys
         */
        public Map<String, String> split(CharSequence sequence)
        {
            Map<String, String> map = new LinkedHashMap<>();
            for (String entry : outerSplitter.split(sequence))
            {
                Iterator<String> entryFields = entrySplitter.splittingIterator(entry);

                checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
                String key = entryFields.next();
                checkArgument(!map.containsKey(key), "Duplicate key [%s] found.", key);

                checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
                String value = entryFields.next();
                map.put(key, value);

                checkArgument(!entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
            }
            return Collections.unmodifiableMap(map);
        }
    }

    private interface Strategy
    {
        Iterator<String> iterator(Splitter splitter, CharSequence toSplit);
    }

    private abstract static class SplittingIterator extends AbstractIterator<String>
    {
        final CharSequence toSplit;
        final CharMatcher trimmer;
        final boolean omitEmptyStrings;

        /**
         * Returns the first index in {@code toSplit} at or after {@code start} that contains the
         * separator.
         */
        abstract int separatorStart(int start);

        /**
         * Returns the first index in {@code toSplit} after {@code separatorPosition} that does not
         * contain a separator. This method is only invoked after a call to {@code separatorStart}.
         */
        abstract int separatorEnd(int separatorPosition);

        int offset = 0;
        int limit;

        protected SplittingIterator(Splitter splitter, CharSequence toSplit)
        {
            this.trimmer = splitter.trimmer;
            this.omitEmptyStrings = splitter.omitEmptyStrings;
            this.limit = splitter.limit;
            this.toSplit = toSplit;
        }

        @CheckForNull
        @Override
        protected String computeNext()
        {
            /*
             * The returned string will be from the end of the last match to the beginning of the next
             * one. nextStart is the start position of the returned substring, while offset is the place
             * to start looking for a separator.
             */
            int nextStart = offset;
            while (offset != -1)
            {
                int start = nextStart;
                int end;

                int separatorPosition = separatorStart(offset);
                if (separatorPosition == -1)
                {
                    end = toSplit.length();
                    offset = -1;
                }
                else
                {
                    end = separatorPosition;
                    offset = separatorEnd(separatorPosition);
                }
                if (offset == nextStart)
                {
                    /*
                     * This occurs when some pattern has an empty match, even if it doesn't match the empty
                     * string -- for example, if it requires lookahead or the like. The offset must be
                     * increased to look for separators beyond this point, without changing the start position
                     * of the next returned substring -- so nextStart stays the same.
                     */
                    offset++;
                    if (offset > toSplit.length())
                    {
                        offset = -1;
                    }
                    continue;
                }

                while (start < end && trimmer.matches(toSplit.charAt(start)))
                {
                    start++;
                }
                while (end > start && trimmer.matches(toSplit.charAt(end - 1)))
                {
                    end--;
                }

                if (omitEmptyStrings && start == end)
                {
                    // Don't include the (unused) separator in next split string.
                    nextStart = offset;
                    continue;
                }

                if (limit == 1)
                {
                    // The limit has been reached, return the rest of the string as the
                    // final item. This is tested after empty string removal so that
                    // empty strings do not count towards the limit.
                    end = toSplit.length();
                    offset = -1;
                    // Since we may have changed the end, we need to trim it again.
                    while (end > start && trimmer.matches(toSplit.charAt(end - 1)))
                    {
                        end--;
                    }
                }
                else
                {
                    limit--;
                }

                return toSplit.subSequence(start, end).toString();
            }
            return endOfData();
        }
    }
}
